GARDENING : Puny, Prolific Aphid Brings Gardeners to Their Knees
It was bound to happen--invasion.
You scan the terrain and there they are, aphididae of the order Homoptera, clinging to your favorite rosebushes and doing the two things they do best--eating and birthing babies. This has got to stop, you say, as your roses seemingly shrivel before your eyes. Stoically you gird yourself for battle. Chemical munitions are brought up to the front. The enemy is engaged.
After 10 minutes of fierce hand-to-tarsi combat, the rout is total. The invading hordes are swept from the field, not to mention the petals and stems of your sagging roses. You bask in the triumph of humankind over one of the bug world’s most notorious pests. Your roses are saved. Victory is sweet. Then, two weeks later. . . .
Behold the mighty aphid. Like a zombie on the lam, you never know just where or when it will show up. You are only certain that it will.
Puny, prolific to boot, with a life cycle as complex and shifting as a teen-ager’s social calendar, the aphid as a species survives massacre and murder thanks to an indestructible law of nature--nothing can kill aphids as fast as they can reproduce.
For this reason there isn’t a garden or field on earth--let alone in Orange County--that doesn’t have at least a few aphids hanging around it from time to time. And where there are a few aphids, if left unchecked, there will soon be a lot of aphids.
Remembering that this is a family newspaper, it can be said that aphids are among the most sexually prodigious of creatures. The birds and the bees may do it, even educated fleas may do it, but Cole Porter would have been amazed at the way aphids do it.
The female aphid is an expert at parthenogenesis--the act of single-gender conception. Using this form of reproduction there is no need for a male aphid or the ardors of insect passion; no moonlit trysts among the jasmine, no coy intermingling of antennae, no mating rituals to slow things down.
Virgin live birth is actually a chromosomal cloning of the mother aphid. New offspring are female duplicates of dear old Mom. In a sense, they are dear old Mom. As if this wasn’t enough, females are born pregnant, a neat trick called paedogenesis. The resulting generational scramble means that daughter aphids are not only sisters to their mothers, they are mothers themselves, and their mothers are grandmothers even before their own pregnant daughters--who are their sisters--are born.
If that confuses you, think what it does to the male aphid who is a straightforward type only looking for some way to sabotage all this solo reproduction. He will get his chance, but only during those times of year when the female aphid shifts biological gears from live birth to egg-laying.
Cold and storm can wipe aphids out by the zillions, but not so the weather-resistant black eggs they leave in the protected nooks of tree branches.
With that certain nip in the air, male aphids do their masculine duty by helping to trigger egg-laying in the females. This not only assures survival of the colony during the harsh winter months, it stirs the gene pool by later hatching out male and female aphids of mixed heritage.
Over time there has been a lot of gene stirring going on because aphids today flourish in some 4,000 known species around the globe. Nick Nisson, an entomologist for the Orange County Agricultural Center in Anaheim, says about 120 different kinds of aphids have been identified so far locally--and every one of them reproduces like crazy.
Let’s crunch some numbers.
Say a single female aphid gives birth to an average of 100 pregnant offspring, and that each of these pregnant offspring in turn gives birth to yet more pregnant offspring, and factor in up to 40 birth cycles a year per aphid . . . let’s see, X multiplied by Y, added to Z, carry the four . . . well, it’s a lot of aphids. British aphidologist A.F.G. Dixon calculates about 600 billion in just nine generations--or as little as seven weeks.
So why isn’t the earth, given such mathematical possibilities, covered with a crust of aphids 3 feet thick? Probably because aphids are good to eat. To other bugs, that is.
Given half a chance, any number of bugs will gladly munch an aphid. In fact, the aphid is the Big Mac of the insect world. Billions are served daily.
The ladybird beetle (or ladybug, of nursery rhyme fame) is a voracious predator of aphids. A single ladybug can devastate an entire aphid colony in a matter of days, if not hours. Its culinary gusto is both spectacular and disgusting. Amplified recordings of ladybug feeding frenzies are as delicate as an ax murder in progress.
Parasitic wasps are among the more gruesomely inventive of the aphid predators. Planted by a parent as larva inside a living aphid’s body, these tiny wasps slowly consume their host from the inside out.
At first the aphid is unaware there is an alien on board. In what must be a horrific way for even a bug to go, the aphid swells up like puffed rice, ultimately turning into a dry, hollow mummy from which an adult wasp will emerge, ready to infest still other aphids with parasitic young of its own.
Sometimes aphids will leap to their doom rather than play the part of movable feast. Once on the ground they quickly dehydrate. It is death not only for the aphid, but also for the invading parasite. The aphid dies a hero’s death, having saved the rest of the colony from the enemy within.
Short of suicide, aphids are virtually defenseless against other insects in the hunt for a quick meal. They usually cling backward to stems and leaves to get a good look at whatever may be crawling up to eat them.
This may not improve their chances of survival, but at least they know whether they’re on that day’s menu.
Aphids are part of that grand family of insect sapsuckers, Homoptera. As such, they do not eat a plant as much as they suck it dry using a syringelike mouth. For this reason they have become the storm troopers of plant disease.
Entomologists estimate that fully 60% of all plant viruses are spread by aphids. The aphid’s feeding tube can inject disease like a drug addict passing around an infected needle. Aphid infestations can cut crop yields by 25% to 50%.
Aphids also excrete a sugary waste product euphemistically called honeydew. Honeydew droppings often promote the growth on plant leaves and stems of a dark fungus called sooty mold that blocks the sun’s rays and reduces the photosynthesis vital to plants.
Disease and honeydew blackout combined with a healthy appetite make the aphid a formidable foe in any garden or field.
While it is bad enough that aphids can crawl all over the place spreading vegetative havoc, at various times of the year females give birth to a winged variety. And an aphid with wings is a highly mobile aphid.
Drain enough nutrients from the host plant and soon winged aphids are soaring off in search of juicier pastures. Overcrowding will also induce airborne exodus. Pack 4 quarts of aphids onto a 3-quart bush and it’s every aphid for itself.
Insect scientist Nisson says there is an aphid for almost any form of vegetation. Variations are common. Some aphids will dine exclusively on one plant host during the summer and switch to an entirely different host during the winter. Some aphids are picky eaters; others enjoy a garden smorgasbord.
Most home gardeners recognize the more common species of aphids, such as the pear-shaped, greenish-pink rose aphid. Other aphids have a distinct mutant cast. Sometimes, when a gardener comes across a mystery species, a pickled specimen is brought to Nisson’s laboratory for identification. Putting name to bug is not always easy, though, because of the aphid’s vast biological diversity.
At times that diversity can seem without end. Part of the problem can be traced to the lack of comprehensive identification catalogues for the multifaceted bugs. Nisson says he’s tempted to list some difficult-to-fix species simply as Aphid, John Doe.
Whether properly identified as Russian aphids, asparagus aphids or even waterlily aphids, chances are the hungry pests will find something to their liking in your garden.
Often they are aided in their blitzkrieg of your tomato plants and petunias by a powerful insect ally--the ant.
Ants and aphids have forged what might be called an insect nonaggression pact. In fact, ants actively protect aphids from other insect predators. They do this in exchange for honeydew--the equivalent of See’s candy to an ant--which they extract by stroking the aphids’ abdomens with their antennae. This milking process has earned aphids the nickname ant cows .
Some ant species will even round up young aphids in a six-legged version of the Chisholm Trail to drive them to more abundant food sources. Along the way the ants will attack any insect trying to rustle a potential aphid porterhouse, biting the intruders until they give up and go away.
Once you’ve got aphids in the garden you need to get rid of them.
A fairly easy form of aphid assassination for the home gardener is dousing the bugs with soapy water, a proven method to strip away the waxy coating that guards the aphids against fatal desiccation.
You can also use a dehydrating dust called diatomaceous earth as a way to dry the bugs to death.
On the wet side, a well-directed garden hose can drown aphids by the millions. Notoriously lousy swimmers, aphids can be washed off stems and leaves without so much as a dog paddle to save them.
If you are the urbane type and cannot recall ever having crossed paths with an aphid, consider that the U.S. Food and Drug Administration allows up to 30 aphids in a 100-gram (3 1/2-ounce) serving of Brussels sprouts--food for thought the next time your kids refuse to eat the stuff.